By trial and errors, you may find that it's only one or two apps that occupy the most resources. I suspect some programmers don't really know what "background" means. For me it totally was a weather app, shipping with the phone.
Anyway the certainity of what happened is still not definitive, let's not depict him as a murderer or a terrorist until then.
These are some topics I've always been curious about, just for the sake of knowledge, and not to endorse them in any way, and that I never looked up, not even on wikipedia, for fear of being "flagged" or whatever:
- pipe bomb construction. Is really that easy to build one as they do in movies? Should I be worried that any psychopath could build one?
- mein kampf. What was going on in that man's mind?
I could think of many other ones... And consider that I don't even live in America.
Moreover, I think this issue is one of the most critical ones for the future of the world as we know it.